Hydrolysis acceleration method of cellulose in organic sludge including food residue

Abstract

To provide a hydrolysis acceleration method of cellulose for decreasing molecular weight of cellulose in an organic sludge and a food residue while suppressing the carbonization rate.SOLUTION: In a hydrolysis acceleration method of cellulose with a carbon rate not exceeding 50% by hydrolysis treatment of an organic sludge including a food residue by a super heated steam reaction at 200°C or under while maintaining a water content of around 50% in the presence of a blended reaction acceleration agent including a crushed powder having an average grain size of 10 mm±5 mm in length including saw dusts, wood waste chips, dry straw, chaff, branches, barks, wood chips, and dry plants as the main component, in which the organic sludge is subjected to a contact reaction with a super heated steam of 300°C or under in a reactor for hydrolysis at 200°C or under so as to decrease molecular weight to hemicellulose. The reactor is assembled with a ribbon blender formed by providing an inner blade 152 and an outer blade 153 around a main inertial axis. A counter flow stirring motion wherein a stirred product flows to the inside by the outer blade, thus strong collision repeatedly occurs while the stirred product flows to the outside by the inner blade to collide with a side case and moves to the outer blade repeatedly occurs.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for promoting cellulose hydrolysis of organic sludge containing food waste, which is produced by an activated sludge process or the like. [Background technology]

[0002] Organic sludge is produced in facilities and equipment that treat wastewater contaminated with organic matter (sewage treatment plants, food factories, animal farms). Most organic sludge is incinerated or dried and disposed of in landfills. However, in recent years, the government has encouraged its use as a raw material for organic fertilizer, both to reduce CO2 emissions through incineration and to recycle it for effective use. However, organic fertilizers do not have an immediate effect after application; most are slow-acting, beginning to work after 30 to 40 days as they are decomposed by microorganisms in the soil. The inventors have proposed a technology for producing organic fertilizer by adding an approximately equal amount of cellulose substrate material (such as sawdust, straw, or rice husks) to organic waste, adding microorganisms that ferment and decompose organic matter, adjusting the moisture content, and then fermenting the sludge (Patent Document 1). However, this method requires time for pretreatment and fermentation of the organic waste, requiring up to four months to produce organic fertilizer. Furthermore, this lengthy fermentation process produces unpleasant odors, which poses environmental concerns.

[0003] Therefore, a method for promoting fertilization has been proposed in which organic waste is treated in high-temperature, high-pressure steam at a temperature range of 150 to 250°C under a pressure range of 15 to 25 kg / cm2 (Patent Document 2). However, the carbonization rate exceeds 50%, and good organic fertilizer is not produced. Therefore, as an improvement, a method has been proposed in which heated steam at 150 to 250°C is supplied under a reduced pressure of 40 to 80 Torr to hydrolyze the waste (Patent Document 3). On the other hand, a method has also been proposed in which treatment is carried out in a subcritical state at a high temperature and pressure of 15 to 40 atmospheres and 200 to 250°C to hydrolyze the polymer compounds in the organic waste and rapidly carry out the subsequent fermentation treatment (Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] PCT / JP98 / 02655 publication [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-55078 [Patent Document 3] Patent Application No. 2011-92938 [Patent Document 4] JP 2018-70386 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, they discovered a problem with the method using heated steam for decompression: the reduction of molecular weight of cellulose was insufficient. On the other hand, the latter method of treatment under subcritical conditions is advantageous for reducing the molecular weight of cellulose, but they also found a problem with the high carbonization rate of cellulose because the treatment is performed under subcritical conditions at high temperature and pressure.

[0006] Therefore, as a result of intensive research, the present inventors have come to the conclusion that in order to reduce the molecular weight of cellulose in organic matter while suppressing the carbonization rate of cellulose, it is necessary to carry out the hydrolysis reaction at a low temperature in combination with the physical condition of countercurrent stirring in a sufficient superheated steam space using a ribbon blender, while promoting the reaction using a cellulose substrate material such as sawdust, maintaining the moisture content at around 50%, preferably above 50%, and using a superheated steam reaction at a low temperature.Based on this finding, an object of the present invention is to provide a method for promoting cellulose hydrolysis that reduces the molecular weight of cellulose in organic sludge and food waste while suppressing the carbonization rate. [Means for solving the problem]

[0007] The present invention is a method for adding a cellulose substrate material to organic sludge in a volume ratio of 2:1 to 1:2, maintaining the moisture content of the cellulose substrate material at around 50%, and providing an agitation means consisting of a ribbon blender. A superheated steam space of 50% or more is provided in the reactor, and the cellulose is stirred and mixed while undergoing a continuous or intermittent contact reaction with superheated steam at 300°C or less, hydrolyzing the cellulose at 200°C or less, and reducing the molecular weight of the cellulose to hemicellulose while suppressing the carbonization rate of the cellulose to 50% or less. The ribbon blender is characterized by being configured with inner blades 152 and outer blades 153 provided around a main shaft 151, and the agitated material flows inward by the outer blades 153 closer to the case, causing repeated strong collisions, while the agitated material flows outward by the inner blades 152 closer to the main shaft 151, where it collides with the side case and moves to the outer blades, repeating a countercurrent agitation motion.

[0008] In the present invention, the organic sludge refers to activated sludge from domestic wastewater such as CP, sewage, and human wastewater, activated sludge from food factories such as food wastewater, and activated sludge from organic chemical processes such as organic chemicals, and includes various food residues.

[0009] In the present invention, the cellulose substrate material includes a plant-based cellulose substrate material whose main component is crushed pieces having an average particle size of 10 mm±5 mm in length, including sawdust, buckwheat husks, wood chips, straw, rice husks, branches, bark, wood chips, and dried grass.

[0010] In the present invention, food waste, i.e., food residue, can be blended as a superheated steam reaction decomposition accelerator in order to adjust the components.

[0011] After the cellulose has been broken down into smaller molecules according to the present invention, fermentation is carried out by adding a mixture of bacterial cells and molasses and rice bran. Preferably, the cellulose substrate material is mixed with the organic sludge treatment product of the present invention in a volume ratio of 2:1 to 1:2, and one or more microorganisms having fermentative decomposition properties are selected from the group below and used for fermentation treatment. Note Bacteria: Bacillus subtilis;Bacillus stearothermophilus;Clostridium thermocellum, Mold: Aspergillus oryzae;Aspergillus niger;Aspergillus fumigatus;Chaetomium thermophile;Humicola lanuginosa;Rhizopus javanicus, Yeast: Candida glabrata;Debaryomyces hansenii;Hansenula anomala;Pichia membranaefaciens;Rhodotorula glutinis;Saccharomyces cerevisiae, Actinomycetes: At least one microorganism selected from the group consisting of Actinobifida dichotomy; Streptomyces griseus; Streptomyces thermophilus; Thermoactinomyces vulgaris; Thermomonospora glaucus; and Monascus sp. [Effects of the Invention]

[0012] According to the present invention, 1) a cellulose substrate material is blended as a reaction accelerator to maintain a moisture content of approximately 50%, i.e., 40-75%, preferably 50% or higher, while the superheated steam treatment is performed. This achieves chemical reaction conditions such that high-molecular-weight cellulose is hydrolyzed at 200°C or lower, even when superheated steam up to 300°C is used. 2) This physical condition, combined with countercurrent mixing using a ribbon blender in a reactor with a heated steam space of 50% or higher, suppresses the carbonization rate and reduces the molecular weight. The stirring operation in the present invention is characterized by being performed using a ribbon blender configured with inner blades 152 and outer blades 153 around a main shaft 151, as shown in Figure 3(b). The outer blades 153, which are closer to the case, drive the agitated material inward, causing repeated strong collisions. Meanwhile, the inner blades 152, which are closer to the main shaft 151, drive the agitated material outward, where it collides with the side case and moves to the outer blades, repeating this countercurrent stirring motion. Therefore, the hydrolysis reaction is carried out at 200°C or less, and the carbonization rate is suppressed while the molecular weight is reduced. Therefore, it can be used as a natural fertilizer as is, but to impart a fragrance, it is recommended to subject it to fermentation treatment. The fragrance is thought to be due to the production of volatile organic acids and the reaction of organic acids with alcohol to produce esters. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a process diagram showing an organic sludge treatment system of the present invention, comprising a drying deodorization treatment, a superheated steam decomposition treatment, and a fermentation treatment. [Figure 2] FIG. 2 is a schematic diagram of an apparatus used for the superheated steam treatment in FIG. 1. [Figure 3] FIG. 3(a) shows a control system diagram of the reactor of FIG. 2, and FIG. 3(b) is an operational diagram showing the operation of the ribbon blender. [Figure 4] A comparison diagram of the heat capacity of superheated steam and hot air. [Figure 5] This is a comparison diagram of the temperature rise of superheated steam and hot air. DETAILED DESCRIPTION OF THE INVENTION

[0014] In the present invention, organic sludge obtained by the activated sludge method is used, and is treated in the system shown in FIG. 1 in the order of drying deodorization treatment 200 → superheated steam decomposition treatment 100 → fermentation treatment 300. In the first drying process, a rotary kiln is preferably used for large-volume drying, and hot air and superheated steam are preferably used as the heat source. To improve drying efficiency, it is recommended to incorporate a cellulose substrate material. Examples of the cellulose substrate material include plant-based cellulose substrate materials such as sawdust, buckwheat husks, wood chips, straw, rice husks, branches, bark, wood chips, and dried grass, and are crushed powders with an average length of 10±5 mm.

[0015] Next, in the superheated steam treatment process, a superheated steam treatment furnace is used as shown in Figure 2. Superheated steam has a higher calorific value than hot air as shown in Figure 4, and has a temperature rise efficiency as shown in Figure 5. In the superheated steam furnace, the superheated steam comes into contact with and penetrates the organic waste being stirred inside the furnace, so the organic matter can be efficiently heated at low temperatures to decompose polymeric substances and to dehydrate and deodorize it.

[0016] In superheated steam treatment, unlike high-temperature, high-pressure subcritical treatment of organic waste, treatment is performed with superheated steam reaching 300°C. Preferably, the moisture content is maintained at 50% or higher, preventing the hydrolysis reaction by the superheated steam from exceeding 200°C, promoting the degradation of cellulose and preventing the carbonization rate of cellulose from exceeding 50%. In other words, when hydrolyzing using superheated steam, it is important to control the hydrolysis temperature between 200°C and 150°C by taking into account the moisture content of the treated material, adjusting the temperature, supply amount, and continuous or intermittent supply of the superheated steam. At temperatures above 200°C, the carbonization rate of cellulose increases and is likely to exceed 50%. On the other hand, at temperatures below 150°C, the hydrolysis rate decreases, making it difficult to decompose cellulose into smaller molecules within the desired time.

[0017] The superheated steam reactor preferably includes a stirring means consisting of a ribbon blender as a stirring and conveying means, and the reactor preferably has a superheated steam space of 50% or more. Here, a ribbon blender, as shown in Figure 3(b), typically has two horizontal ribbon blades. The outer blades closest to the case drive the material to the inside, causing repeated strong collisions, while the inner blades closer to the main shaft drive the material to the outside, where it collides with the side case and moves to the outer blades. This repeated stirring motion ensures efficient contact and reaction with the superheated steam. By devising the ribbon shape, it is possible to adjust the stirring motion from front to back, inside to outside, and so the material can be conveyed from the IN to the OUT while stirring, but it is preferable to attach a transport roller conveyor to the bottom of the reactor.

[0018] The superheated steam treatment of the present invention can be carried out by connecting two or more superheated steam reactors in series depending on the reaction treatment capacity of each superheated steam reactor, or by repeatedly treating with one reactor. The degree of treatment can be appropriately selected depending on the conditions of the subsequent fermentation treatment.

[0019] The organic sludge to be treated in this invention includes food waste such as vegetable scraps and fish bones discharged in large quantities from supermarkets and other food retailers, sludge generated during sewage treatment from sewage treatment facilities in food factories, and livestock manure discharged from poultry farms and livestock farms. Because these organic sludges have a high moisture content, they have traditionally been incinerated, but in this invention, the superheated steam treatment not only deodorizes the sludge but also breaks down the cellulose into smaller molecules, facilitating the subsequent fermentation process.

[0020] The process of fermenting organic waste is preferably a process of piling up a mixture of pretreated organic waste and wood waste, which is a cellulose substrate material, and culturing it under aerobic conditions while controlling the temperature and moisture content in combination with the cellulose substrate material. This will eliminate any unpleasant odor and further promote the breakdown of cellulose into smaller molecules.

[0021] In an embodiment of the present invention, organic sludge is pretreated by a superheated steam reaction, followed by microbial fermentation to produce cellulose. The pretreated raw material is particularly suitable for breaking down cellulose in sludge discharged from sewage treatment facilities, vegetable waste and fish scraps discharged from supermarkets and other food retailers and homes, and animal or human waste, all of which have been considered difficult to process.

[0022] In carrying out the present invention, a system shown in Figure 1 is used. The system of the present invention comprises a drying lane consisting of a rotary kiln as a drying lane for organic sludge, a superheated steam treatment lane which is a superheated steam furnace, and a fermentation treatment lane. The organic sludge is dried using a rotary kiln before being treated with superheated steam. To improve drying efficiency, it is preferable to use a cellulose substrate material, as it is also used as a dispersion medium in the superheated steam treatment process. Next, in the superheated steam treatment process, a superheated steam reactor 100 shown in Figure 2 is used. The reactor is equipped with a tank 110 for supplying organic waste and a rotor 120 that is motor-driven to supply organic waste to the reactor. The reactor is also equipped with a superheated steam supply means 130, and inside the reactor is a ribbon blender 150 that agitates the organic waste and superheated steam that have been introduced and transports them from the inlet (IN) to the outlet (OUT).

[0023] 3(a), the superheated steam reactor 100 is provided with a superheated steam supply means 130 consisting of a boiler 131 and a superheated steam generator 132 that superheats the steam generated from the boiler 131, and a control panel 140 controls the boiler 131 and the superheated steam generator 132 to supply a predetermined amount of superheated steam to the reactor 130. The control panel 140 also controls a motor 160 that drives a ribbon blender 150 in the reactor to adjust the stirring speed.

[0024] As shown in Figure 3(b), ribbon blender 150 provided inside reactor 130 is configured with inner blades 152 and outer blades 153 arranged around main shaft 151, and the material to be stirred flows inward by outer blades 153 close to the case, causing repeated strong collisions, while the material to be stirred flows outward by inner blades 152 close to main shaft 151, hitting the side case and moving to the outer blades, repeating the stirring motion.

[0025] In the present invention, a superheated steam reactor is used which has a superheated steam supply means which produces superheated steam up to 300°C and injects the superheated steam into the furnace at a predetermined pressure under atmospheric pressure, a stirring and transporting means which stirs and mixes the superheated steam from the superheated steam supply means with organic waste and transports it into the furnace from an inlet IN to an outlet OUT, and a reaction control means 140 which reacts the stirred and transported organic waste with the superheated steam in a temperature range of 150°C to 200°C, and which decomposes, deodorizes, and sterilizes organic sludge at low temperatures of 150°C to 200°C while suppressing carbonization.

[0026] The superheated steam treatment of the present invention maintains a moisture content of 50% in combination with a cellulose substrate material, and by providing a stirring means consisting of a ribbon blender and providing a reactor with a superheated steam space of 50% or more for countercurrent stirring, the reduction of molecular weight to hemicellulose is promoted while maintaining a carbonization rate of 50% or less. The superheated steam reaction at low temperatures appropriately reduces the volume of cellulose in the organic waste, cracking the particles. Furthermore, countercurrent stirring by the ribbon blender in a superheated steam space of 50% or more is thought to promote the reduction of molecular weight. Fermenting organic waste treated in this way enables the fermentation period to be shorter than conventional methods.

[0027] The time for the superheated steam reaction treatment can be determined depending on the moisture content of the organic sludge. For example, it is preferable to treat until the appearance of the mixture of the organic sludge and the cellulose substrate material after treatment turns brown. For example, the heat treatment and pressure treatment are preferably carried out for 20 to 180 minutes, more preferably 20 to 60 minutes. The treatment temperature and treatment time can be determined depending on the moisture content of the organic sludge.

[0028] The superheated steam treated material is fermented using microorganisms. In the method of this embodiment, microorganisms capable of decomposing high molecular weight organic matter contained in organic waste into low molecular weight organic matter are used. Examples of such microorganisms include microorganisms that grow under aerobic conditions. Microorganisms that grow under aerobic conditions include Bacillus subtilis, Bacillus stearothermophilus, Bacillus coagulans, Clostridium thermocellum, Aspergillus oryzae, Aspergillusniger, Aspergillus fumigatus, Lactobacillus sp.1, Lactobacillus sp.2, Lactobacillus sp.3, Pediococcus sp., Pseudomonas sp, Chaetomium thermophile, Humicola lanuginosa, Rhizopus javanicus, Candida glabrata, Debaryomyces hansenii, Hansenula anomala, Pichia membranaefaciens, Rhodotorula glutinis, Saccharomyces cerevisiae, Actinobifida dichotom, Streptomyces griseus, Streptomyces thermophilus, Thermoactinomyces Examples of suitable microorganisms include at least one selected from the group consisting of Thermomonospora vulgaris, Thermomonospora glaucus, and Monascus sp.

[0029] The organic sludge that has been treated with superheated steam is preferably subjected to solid-state culture under aerobic conditions while controlling the temperature and moisture content. In the method of this embodiment, the moisture content is controlled to be around 50%, or 40 to 75% by mass, and the temperature inside the organic waste is controlled to be 55 to 85°C. Temperature control can be achieved, for example, by adjusting the fermentation heat based on the height and width of the organic waste pile and by controlling the frequency of turning.

[0030] In the fermentation process of the present invention, it is preferred to further mix wood waste materials such as sawdust, buckwheat husks, wood shavings, straw, branches, bark, and wood chips with the pretreated organic sludge.

[0031] If the moisture content of the organic sludge after superheated steam treatment is low, it is preferable to replenish the water and perform solid-state culture under aerobic conditions. Because the moisture content of organic sludge before treatment is relatively high, adding a cellulose substrate material can adjust the moisture content to a level suitable for microbial growth. It is recommended to add a fermentation agent (available as TF bacteria from Fukunaga Microorganism Research Institute, Inc., 2705 Funatsu-cho, Himeji City, Hyogo Prefecture) to the cellulose substrate material at a rate of approximately 100 g per ton of material to be treated.

[0032] The nutrients in the fertilizer can also be adjusted with food waste or its dried form. [Example]

[0033] The method for reducing the molecular weight of organic sludge according to the present invention will be explained in more detail below with reference to examples. Organic sludge obtained from a food factory is mixed with sawdust in a 2:1 volume ratio and dried to a moisture content of 50 to 70%. This pretreated material is then treated for 30 to 60 minutes in a pretreatment facility equipped with a superheated steam reactor, as shown in Figure 2. Analysis of the material's components reveals a decrease in nitrogen content along with a decrease in moisture content. This is thought to be due to the formation and sublimation of amino acids associated with the conversion of high molecular weight proteins into peptides. While the extent of cellulose hydrolysis is unclear, the subsequent fermentation process requires at least half the time required for aroma release, demonstrating the promotion of the depolymerization of cellulose.

[0034] After pretreatment, sawdust and fermentation material were added to the organic sludge to adjust the moisture content of the organic waste to 60% by mass. The fermentation material was a mixture of molasses and rice bran in a ratio of 2:1 to 5:1, and Bacillus subtilis, Lactobacillus sp.1, and Aspergillus oryzae were used.

[0035] Solid culture was carried out for 7 days to 1 month while controlling the moisture content to 40 to 75% by mass and the internal temperature to 55 to 85°C, and fermentation was continued for at least 10 days until the aromatic flavor was released.

[0036] The aromatic release is thought to be due to the formation of volatile fatty acids or esters due to the reaction of fatty acids with alcohol as carbohydrates, proteins, and fats are broken down into smaller molecules. Along with the formation of amino acids, this improves the fertilizer properties of the fermented product. [Explanation of symbols]

[0037] ; 100 Superheated Steam Reaction Lane 200 rotary kiln drying lanes 300 Fermentation Lane

Claims

1. A method for promoting the hydrolysis of cellulose in organic sludge, comprising: adding a cellulose substrate material to organic sludge in a volume ratio of 2:1 to 1:2; maintaining the moisture content of the cellulose substrate material at around 50%; providing an agitation means consisting of a ribbon blender; and providing a reactor with a superheated steam space of 50% or more for agitation and mixing; continuously or intermittently contacting the cellulose with superheated steam at 300°C or less; hydrolyzing the cellulose at 200°C or less; and reducing the molecular weight of the cellulose to hemicellulose while suppressing the carbonization rate of the cellulose to 50% or less. The ribbon blender is configured with inner blades 152 and outer blades 153 provided around a main shaft 151; the outer blades 153, which are closer to the case, cause the agitated material to flow inward, resulting in repeated strong collisions; while the inner blades 152, which are closer to the main shaft 151, cause the agitated material to flow outward, where it collides with a side case and then moves to the outer blades, repeating a countercurrent agitation motion.

2. 2. The method for promoting hydrolysis of cellulose in organic sludge according to claim 1, wherein the organic sludge includes activated sludge from domestic wastewater such as CP, sewage, and human wastewater, activated sludge from food factories such as food wastewater, and activated sludge from organic chemical processes such as organic chemical process wastewater.

3. 2. The method for promoting hydrolysis of cellulose in organic sludge according to claim 1, wherein the cellulose substrate material comprises a plant-based cellulose substrate material mainly composed of crushed pieces having an average particle size of 10 mm±5 mm in length, including sawdust, buckwheat husks, wood chips, straw, rice husks, branches, bark, wood chips, and dried grass.

4. 2. A method for promoting the hydrolysis of cellulose in organic sludge according to claim 1, wherein a pretreated dried food waste is added as an accelerator for the superheated steam decomposition of organic sludge.

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